Index: head/devel/mdb/Makefile
===================================================================
--- head/devel/mdb/Makefile
+++ head/devel/mdb/Makefile
@@ -21,6 +21,7 @@
 MAKE_ARGS=	WITH_CTF=yes
 MAKE_ARGS+=	BINDIR=${PREFIX}/bin
 MAKE_ARGS+=	LIBDIR=${PREFIX}/lib
+MAKE_ARGS+=	FREEBSD_SRC_DIR=${SRC_BASE}
 WRKSRC_SUBDIR=	freebsd/cddl/usr.bin/mdb
 CFLAGS+=	-DMDB_PREFIX=\\\"${PREFIX}\\\" -g